The GraphQL type system is described in section 3 of the specification. Per the specification itself,
The GraphQl Type system describes the capabilities of a GraphQL service and is used to determine if a requested operation is valid, to guarantee the type of response results, and describes the input types of variables to determine if values provided at request time are valid.
This feature of the specification for the GraphQL language uses Interface Definition Language (IDL) to describe the type system. This can be used by tools to provide utility function as client code genration or boot-strapping. In a lot of the services and products around GraphQL like AppSync, Hasura, and others you’ll see this specifically in action. Tools that only execute requests can only allow TypeSystemDocument and disallow ExecuteDefintion or TypeSystemExtension to prevent extensions of the type system. If you do this be sure to provide a descriptive error for consumers of your data!
Let’s say you’ve built out your GraphQL API. Now let’s say you want a schema.graphql file but for some reason you don’t have your repo or for some reason it’s not immediately available. What to do? Here are two tools to get a quick schema of your GraphQL API by pointing them at your API and letting them introspect against it!
For both of these you’ll need to have NPM installed, which I’ll just assume you do if you’re dealing with GraphQL. If you don’t, head on out and get NPM and Node.js installed for good measure, and per my suggestion do yourself a favor and pick a version manager. I generally use nvm, check out details on install NVM here.
GraphQL, a query language and execution engine is described in this specification based on capabilities and requirements of data models for client-server applications. This article details and elaborates on the specification, the features and capabilities of GraphQL and implementations. I hope this collection of details around the GraphQL Specification can be used as a reference and launch point into learning about GraphQL use, implementation – server and client side – and ongoing references during future specification additions or changes!